/*
 * tinfzlib - tiny zlib decompressor
 *
 * Copyright (c) 2003-2019 Joergen Ibsen
 *
 * This software is provided 'as-is', without any express or implied
 * warranty. In no event will the authors be held liable for any damages
 * arising from the use of this software.
 *
 * Permission is granted to anyone to use this software for any purpose,
 * including commercial applications, and to alter it and redistribute it
 * freely, subject to the following restrictions:
 *
 *   1. The origin of this software must not be misrepresented; you must
 *      not claim that you wrote the original software. If you use this
 *      software in a product, an acknowledgment in the product
 *      documentation would be appreciated but is not required.
 *
 *   2. Altered source versions must be plainly marked as such, and must
 *      not be misrepresented as being the original software.
 *
 *   3. This notice may not be removed or altered from any source
 *      distribution.
 */

#include "tinf.h"

static unsigned int read_be32(const unsigned char *p) {
  return ((unsigned int)p[0] << 24) | ((unsigned int)p[1] << 16) |
         ((unsigned int)p[2] << 8) | ((unsigned int)p[3]);
}

int tinf_zlib_uncompress(void *dest, unsigned int *destLen, const void *source,
                         unsigned int sourceLen) {
  const unsigned char *src = (const unsigned char *)source;
  unsigned char *dst = (unsigned char *)dest;
  unsigned int a32;
  int res;
  unsigned char cmf, flg;

  /* -- Check header -- */

  /* Check room for at least 2 byte header and 4 byte trailer */
  if (sourceLen < 6) {
    return TINF_DATA_ERROR;
  }

  /* Get header bytes */
  cmf = src[0];
  flg = src[1];

  /* Check checksum */
  if ((256 * cmf + flg) % 31) {
    return TINF_DATA_ERROR;
  }

  /* Check method is deflate */
  if ((cmf & 0x0F) != 8) {
    return TINF_DATA_ERROR;
  }

  /* Check window size is valid */
  if ((cmf >> 4) > 7) {
    return TINF_DATA_ERROR;
  }

  /* Check there is no preset dictionary */
  if (flg & 0x20) {
    return TINF_DATA_ERROR;
  }

  /* -- Get Adler-32 checksum of original data -- */

  a32 = read_be32(&src[sourceLen - 4]);

  /* -- Decompress data -- */

  res = tinf_uncompress(dst, destLen, src + 2, sourceLen - 6);

  if (res != TINF_OK) {
    return TINF_DATA_ERROR;
  }

  /* -- Check Adler-32 checksum -- */

  if (a32 != tinf_adler32(dst, *destLen)) {
    return TINF_DATA_ERROR;
  }

  return TINF_OK;
}
